1. Field of Invention
The present invention relates to a printer that prints by selectively heating thermal paper that reacts to heat energy.
2. Description of Related Art
Thermal printers are one type of printer known from the literature. Thermal printers print using a direct thermal printing method that prints to thermosensitive paper (commonly called “thermal paper”) as a result of the print head, which has small heating elements to which an electrical current is selectively applied arranged in a line, selectively fusing the color layers of the thermal paper, causing the heated dot to change to a particular color. As taught in Japanese Unexamined Patent Appl. Pub. JP-A-2004-98699 and Japanese Unexamined Patent Appl. Pub. JP-A-2001-322304, the thermal print head that prints by this direct thermal method has a pressure mechanism that urges the print head towards an opposing platen disposed to a heat radiation plate. The thermal paper is inserted between the thermal head and the platen, and is selectively heated while pressure is applied by the pressure mechanism to selectively fuse the color layers of the paper to print. The printed thermal paper is then conveyed outside the printer with the side of the paper having the color layers in contact with a guide member disposed to the heat radiation plate downstream from the thermal head.
Label paper is one type of thermal paper that is printed by such thermal printers. Such label paper has an adhesive coating on the opposite side as the side containing the color layers, and a web (liner) that protects the adhesive area. Information is printed in the thermosensitive area of the label paper, and the labels can then be peeled from the liner and applied to some other object.
If the platen is disposed to the main cover of the thermal printer, a mechanism for preventing the cover from hitting and damaging the thermal head when the cover is closed is needed. So that pressure can be accurately applied to the thermal paper when printing, the platen opposing the thermal head must be protected from scratching and damage particularly in the middle area where printing becomes lighter. This is commonly accomplished by providing a guide member to guide the platen to a prescribed position. However, as the cover is repeatedly opened and closed and repeatedly contacts the guide member, the platen gets scratched and damaged so that pressure is not accurately applied to the platen, contact between the platen and thermal paper therefore deteriorates, and print defects occur.
A newer type of thermal paper is linerless label paper that does not have a liner protecting the adhesive area. However, because linerless label paper is wound into a roll and the adhesive side of the paper is necessarily wound against the color layer side of the paper, a small amount of the adhesive from the adhesive side inevitably adheres to the surface of the color layer side behind the adhesive side. When the surface containing the color layers of the printed linerless label paper then passes over the guide member, the adhesive sticking to the color layer surface transfers to the guide member. As the adhesive accumulates, smooth transportation of the thermal paper is impeded, contact between the thermal head and the thermal paper deteriorates, and print defects occur.